Design and development of high entropy matrix - ceramic reinforced composites for structural applications

Abstract

Face-centered cubic (FCC) CoCrFeNi high entropy alloy (HEA) was most commonly studied HEA. This HEA has outstanding ductility at room temperature as well as at cryogenic temperatures but has low strength. An innovative composite approach was utilized to obtain better set of strength and ductility. Varying quantities of SiC and TiB2 particles were incorporated into HEA via arc melting route. The interaction of ceramics with constituent elements of HEA matrix caused their decomposition during melting, leading to in situ formation of carbides, silicides and borides. A range of mechanical properties was observed in the composites of high entropy alloys. The carbide reinforced high entropy composites developed because of SiC addition showed the values of yield strength, % elongation and hardness ranging from 277 MPa, >60% elongation and hardness 250 HV to high yield strength value of 2522 MPa with 6.19% elongation and755 HV hardness. While boride reinforced high entropy composites displayed a range from 180 MPa to 1282 MPa yield strength, % elongation over 60 to 3.4% and values hardness from 200 HV to 750 HV, respectively. Ashby's maps of mechanical properties across various materials revealed that properties of high entropy composites fell within a range that was earlier considered unachievable in HEAs. The ceramic reinforced high entropy composites demonstrated remarkable set of superior yield strength and % elongation as a result of f uniformly dispersed carbides and borides i.e., 1200 MPa and 37 % elongation for 6 weight % SiC addition and 918 MPa and 30 % elongation for 6 weight % TiB2 addition. The incorporation of SiC improved the resistance of composites to oxidation at 900°C because of formation of protective SiO2 and Cr2O3 oxide layers. The introduction of TiB2 enhanced the corrosion resistance of the composites in a 3.5 weight % NaCl solution. The assessments of isothermal oxidation and corrosion resistance have illuminated the prospective utility of these high entropy composites within challenging structural conditions. This research underscores the promising composite approach in achieving better combination of strength and ductility in high entropy alloys for use in demanding structural applications.